The long-term objective of this work is to determine how lipid and protein structures are altered upon their mutual interaction in a hierarchy of model membrane systems of increasing complexity, and how these alterations are related to function. Novel FT-IR experiments yield quantitative information about membrane lipid conformations in phospholipid vesicles or monolayer films. The developed protocols are applicable to more technically difficult but physiologically relevant experimental paradigms such as living cells. Two specific aims, each with physical and biological components, are planned: (AIM 1, PHYS.): To determine the number of 1-, 2-, and 3-bond acyl chain conformational states in structurally disordered, biologically relevant phases such as the Lalpha or the H/II. (AIM 1, BIO.): To detect quantitative IR conformational marker bands in the live cell membranes of a microorganism (A. laidlawii B). Chain conformations in intact cells will be studied under a variety of conditions of interest including its response to altered growth phases and temperatures, and addition of functionally disruptive agents. (AIM 2, PHYS.): To develop FT-IR for the molecular characterization of conformational and orientational order of both lipids and proteins in situ in monolayers at the A/W interface. We have built a novel external reflection (IRRAS) apparatus that has permitted acquisition of the first protein monolayer IR spectra. (AIM 2, BIO.): To evaluate structure/function relationships in the physiologically essential lung surfactant system. IRRAS provides a unique test of the "squeeze-out" hypothesis of pulmonary surfactant function. This hypothesis requires that the major lipid component of surfactant becomes enriched at the A/W interface during successive expansion-compression cycles (exhalation- inhalation cycles in vivo) to produce the requisite low surface tension. We will examine the occurrence of squeeze-out, its dependence on lipid structure and conformation, and the ability of surfactant proteins, to alter squeeze-out parameters. These experiments will permit rational design of therapeutic agents for infant respiratory distress syndrome (RDS) and its adult counterpart (ARDS).